Blasting operations often involve initiation of a plurality of explosive charges. Typically, blastholes are drilled into the rock to be blasted. The blastholes are at least partially filled with explosive material, and one or more initiation means are associated with each explosive charge. Command signals generated by a central command station are transmitted to one or more blasting machines, each in signal communication with one or more initiation means in blastholes at the blast site. The command signals can arm, disarm and fire the initiation means as appropriate.
The quality of the blasting event can be measured by the degree and efficiency of rock fragmentation. Many factors influence the efficiency of blasting. Some of the most important factors include the arrangement of the explosive charges at the blast site, and the relative timing of initiation of the explosive charges. Such factors influence the co-operation of stress fields propagating from initiation of each explosive charge in each blasthole. Numerous blasting methods are known in the art that specify the arrangement and/or relative timing of explosive charges, which attempt to optimise rock fragmentation without the need for excessive quantities of explosive material.
In one example, U.S. Pat. No. 3,295,445 issued Jan. 3, 1967, discloses a method of blasting in which a multiplicity of charges are separated into groups of charges. The charges in each group are detonated at substantially the same time, and the groups are detonated sequentially by means of delay detonators in such a manner that groups of charges not yet fired are initiated before proximate charges in adjacent groups are fired.
In another example, U.S. Pat. No. 3,903,799 issued Sep. 5, 1975 provides for a method of blasting which allows greater amounts of explosives to be detonated at one shooting than was previously possible while at the same time holding the maximum vibration produced at or below levels produced by a single detonation. A plurality of charges are arranged in spaced apart rows with the detonations within a row being detonated with time delays of 10 ms or more and with the detonations between successive rows being detonated with time delays of from 25 to 150 milliseconds.
In another example, a paper entitled “Precision detonators and their applications in improving fragmentation, reducing ground vibrations, and increasing reliability—a look into the near future” by R. Frank Chiappetta, presented at the Blasting Analysis International conference, Nashville, Tenn. (June 1992) discloses numerous methods of blasting and is incorporated herein by reference. The disclosure includes discussion of the use of explosive columns of material, wherein the columns are embedded in predrilled blastholes. As is typical in the art, a primer triggers actuation of the column of material at one end, causing the material to produce a detonation head, which burns along the column away from the primer. Shockwaves are propagated from the detonation head in such a manner that the shockwaves exert their greatest stress perpendicular to the primary shockwave. The reference discloses the use of primers positioned at opposite ends of columns of explosive materials in adjacent blastholes. In this way, interference of opposing shockwaves propagated from the adjacent blastholes can cause rotational motion giving rise to increased tossing and shearing of the rock located between the blastholes.
In another example, U.S. Pat. No. 5,388,521 issued Feb. 14, 1995, discloses a method of blasting involving one or more arrays of elongate, chemical explosive charges so as to produce relatively low levels of ground vibration. The orientation and velocity of propagation of vibration are such that, at a selected outlying location, the onset of vibration from explosion of the first negligibly small increment of the charge arrives a finite time before that from explosion of the last negligibly small increment. The charges of each array are fired in accurately timed sequence, with the times between initiations chosen so that, at the outlying location, the onset of vibration from explosion of the last small increment of charge, except the last charge, arrives a negligibly small increment of time before the onset of vibration from explosion of the first small increment of the succeeding charge. All arrays are designed to give equal times between onsets of vibration from the first and last charge increments to explode.
In another example, International Patent Publication WO02/057707 published Jul. 25, 2002, discloses methods of blasting involving precision timing of electronic detonators. The methods make use of precision timing to control the generation and formation of the rock pile resulting from a blasting event. The timing and arrangement of blastholes at the blast site can increase or decrease rockpile displacement as desired.
In another example, U.S. Pat. No. 6,460,462 issued Oct. 8, 2002, discloses a method of blasting rock or similar materials in a surface and underground mining operations in which neighbouring bore holes are charged with explosives and primed with detonators. The detonators are programmed with respective delay intervals according to the firing pattern and the mineral/geological environment and the resulting seismic velocities.
Although significant advances have been made in blasting methods over recent years, there remains a continuing need to develop improved methods of blasting that offer efficient rock fragmentation without the need for excessive quantities of explosive materials. Moreover, there remains a continuing need to develop methods of blasting in which the rock is properly fragmented without excessive impact upon the surrounding environment, for example through excessive ground vibrations.